A number of active agents are applied to the exterior surfaces of plants for the purpose of affecting or protecting the plant. Plant growth regulating agents are applied for killing the plant or regulating (e.g., stunting or encouraging) its growth activity. Plant growth regulating agents encompass those agents known to act as herbicides as well as those acting as fertilizers and plant growth hormones. Systemic insecticides for plants are applied to protect the plant against insect damage.
Almost all externally applied active agents must first enter the plant metabolism through various transport and absorption mechanisms before the agent can have its intended effect. The absorption and assimilation of the applied agents is hindered by a natural waxy outer coating on most plant external surfaces. In general, agents that are not readily assimilated into the plant require higher application rates or must be applied in combination with agents that increase the residence time on the foliage to accommodate a slower assimilation rate. Neither solution is entirely satisfactory since both higher application rates and increased residence times on the plant foliage present increased risks of environmental contamination as well as increased risks to the applicators. Indeed, some otherwise useful herbicides and plant growth regulating agents have received maximum application rate limits due to such problems.
Surfactants have been commonly used to increase the wetted surface area of the plant's outer surface. The increased area thus increases the absolute amount of applied agent that is absorbed in a unit of time. The most commonly used surfactant for plant growth regulating agents is a product known as ORTHO X-77.TM. containing 70-75% ethoxylated octylphenol, 15% free fatty acids, and 10% isopropanol. It is believed that the isopropanol component of X-77.TM. partially dissolves the waxy outer coating to permit the applied agents to more easily penetrate into the plant tissues. Isopropanol, however, poses certain risks of flammability in use and in product storage.
It would be desirable to have a means for reducing the amount of active agents that are applied to the external surfaces of plants without sacrifice in efficacy.
It would also be desirable to have a means for increasing the efficacy of externally applied active agents when used at the same application rate as is conventionally used.